Note: Descriptions are shown in the official language in which they were submitted.
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A SPOILAGE INDICATING DEVIOE FOR FOOD CONTAINERS
BACKGRO~D OF l~IE INVENTION
1. Field of the Invention.
The present invention relates to detection and
warning systems for controlling the state of freshness of
food-stuffs and biological preparations which are stored in
food cnnt~inPrs during some time oefore consumption, which
food cnnt~;nPrs are preferably to be purchased by final
consumers who are warned by the visual indication of any
harmful bacterial process inside the food package. Most
preferably, the invention refers to a spoilage visual
indication device for use in milk-based-product cnnt~inprs~
Although the present invention will be disclosed in
relation to the diary industry, the same is applicable to
any field of the food industry where the state of freshness
of stored products must be constantly monitored
2. Description of the Prior Art.
One of the most important parameters to be
monItored during conservation of products is the acidity
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level of the products. The suitable acidity will depend on
the kind of product, thus a high acid level must be kept
for pickles to avoid bacterial and fungi multiplication,
while a low level must be controlled for a diary product to
avoid spoilage under a high level of acidity.
Diary products, such as milk, butter, cream, yogurt
and the like are extremely susceptible to decomposition
and, therefore, control must be kept on the pX which must
be, in the fresh state of milk, for example, of 6.5 to 6.6.
The pH level is affected, in diary products, by the undue
bacterial multiplication, such as the lactobacilli, which
causes the pE level to decrease whereby the product is
excessively acid and below the acceptable conditions for
human consumption. Generally, the freshness of the milk is
controlled only during the bulk processing so that the
quality thereof is high at the time the bottled milk or
milk-based packaged product is delivered through the
distribution system to customers. However, under the
distribution conditions the products may be exposed, during
long periods of time, to undue high temperatures which
cause the bacteria to undergo an excessive multiplication
whereby the milk becomes unsafe and spoiled well before the
date marked generally in the cr~nt;3;nF~r for indicating an
estimated freshness time period within which the product
must be consumed. This period of time, marked in the
package, is estimated by the manufacturer on the basis of
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tests and tables, but the changing weather conditions, the
different geographical areas and freezing interruptions may
alter the e~pected freshness life of the product, and that
period is generally shorter than expected.
In some cases the organoleptic characteristics of
the product depends on the solubility and dispersion
capability of the proteins and/or polymers in the packaged
product. The physicochemical characteristics of the
lacteous proteins, such as the solubility based on the pH o
zero-electric-charge point, are sensitive to the solution
conditions, the pH, salt concentration, other proteins and
carbohydrates, etc. When orrllrr;nri changes in the product
due to the bacterial activity, proteins may lose their
emulsifying and/or stabilizing functions for the product
emulsion or dispersion, as well as the proteins may undergo
a coagulation or precipitation whereby the organoleptic
features are lost, although the product may be in
acceptable human consumption conditions.
Under the above conditions, neither the retailer
nor t~Le f inal consumer have the means to be aware that the
product is under a minimum riuality for human consumption.
This is why many attempts have been made ln order to have a
reliable way and systems for the cfmsllmPrs to deterrnine
whether a diary product is in conditions to human
consumption and in a high rluality state.
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U.S. Patent N 2,485,566 refers to a method and
device for indicating spoilage, and more particularly
refers to an indicator system for indicating harmful
bacterial processes inside a food package, the system
consisting of a transparent cell associated with the
package, in which a bacterial process analogous to that
occurring inside the package is visually observable. A pX-
change-responsive indicator reacts to bacterial or
enzymatic change of the pX produced by a strain of
bacteria, inside the cell, which is activated by the same
temperatures which bring about the harmful process inside
the f ood package . The property of bacteria to produce
enzymes is well known, and such enzymatic action is
visually indicated as a result of the change of the pH of
the indicator.
The above ref erred indicator comprises a paper dyed
or impregnated with a neutral or weakly ~1 ki~-, n.- solution
of a suitable pH indicator such as brom cresol green The
dyed paper is also coated or saturated with a nutrient
culture medium and inoculated with an acid-forming bacteria
such as one of the lactobacilli, and covered with a film of
cellophane. The indicator is placed ~n a package, in a
visible manner so that, when the temperature of the package
becomes sufficiently high, the bacteria in the indicator
will multiply sufficiently to produce enough lactic or
acetic acid to transform the color of the indicator dye
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used from its blue i3lki~1 ;n~ color to its yellow acid color.
T~e strain of bacteria used and the quality of alkali or
buffering salt employed in the uutrient must be carefully
adjusted so that the time for the development of the acid
color corresponds with the minimum time and temperature for
undesirable development of any toxic bacteria in the
packaged product. This indicator, therefore does not react
upon the direct spoilage of the product but upon the room
conditions where the product is stored. If, for any
reasons, the temperature within the indicator containing
cell differs from the temperature in the product mass the
indicator reaction will not reflect the exact state of
freshness of the product.
US Patent N3,067,015 discloses a spoilage
indicator including a transparent window mounted in a wall
of a cnnt~in~r, an indicator element positioned in said
cnn~;~;n~or behind said window, a diffusion sheet being
unidirectionally permeable to gases but impermeable to
liquids and solias, said indicator element being sealed
between said diffusion sheet and said window, said
indicator element including a color changing chemical
substance reactive to gases in said rr,n~linF~r, particularly
C2 resulting from the spoilage of ~ood in the C--n~ilin~r,
whereby said substance when spoilage occurs undergoes a
color change observable through said window.
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US Patent N4, 003, 709 discloses the detection of
C2 gas in food r~ntA;nPrs by using a microporous plastic
material to permit C02 gas to reach a C02 detector while
preventing passage of liquids and solids. Thus, liquids and
solids cannot penetrate the microporous plastic and the C02
detecting medium is not in cQntact with the food contents.
More particularly, such a detecting system provides a
liquid impermeable pouch in which a liquid C02 detecting
solution rr)ntA;n;ng calcium hydroxide is entrapped. The
solution provides a visually observable change when the
concentration of C02 rises substAnt;Al ly above a normal
concentration. One side of the pouch is formed of a plastic
material defining a window through which the ;n~ AtOr may
be observed . Another portion of the pouch i8 f ormed of the
gas permeable mi~LU~UULUUs plastic mAtPr;Al. The C,-ntA;nPr
has an opening formed therein and the pouch is sealed into
and over the opening so that the inert plastic material
seals the opening and the microporous plastic portion is
inside the ~-,,ntA;nPr in at least gaseous contact or
communication with the food contents. Thus, as C02 gas is
generated it will pass through the mi-:LU~ULUUS plastic and
react with the calcium hydroxide to precipitate calcium
carbonate. This causes the solution to change from clear to
milky white, and this change is readily observable from
outside the ,,ntA; nPr by looking through the window . When
the gas is produced, the observer sees the color change
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indicating that the food is probably spoiled and should not
be consumed. Again, as far as the pouch material is
-~hl e to liquids this indicator does not enter into
direct contact with the packaged product and only reacts
upon C02 generation.
The above indicating devices only react upon the
presence of C02 gas generated upon undue bacterial
multiplication but this is not an index of the acidity or
alkalinity of the product. Since the acceptable pH level
varies from product to product it would be very convenient
to count on an indicator which may be adapted to indicate
the prF~ t~rm;n~ pH level of a desired product to be
monitored so as to keep a control thereon not only in
connection wlth its quality to human conditions but also in
connection to its organoleptic features and proteins
quality .
The conv,~n~ n~l gas detecting devices, in
addition, must be prevented from entering into contact with
the liquid stored in the ~mt~;n~rs as far as the C02
detector may be affected by the solids or liquids. To this
purpose the above disclosed C02 detectors are closed within
a microporous membrane ; , e '~hl e to liquids but the C02
gas generated will pass through the membrane and react to
the indicator to provide the visual indication. The
membrane, however, must also be prevented from entering
into contact with the stored liquid because af ter many
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times the liquid is in contact with the microporous
membrane a covering film from the liquid may be deposited
on the membrane and the microporous may be closed by the
solidified or crystallized liquid particles and solids.
Wit~l the microporous membrane thus blocked no C02 gas will
be able to pass through the membrane and enter the cell to
react with the indicator. It would be therefore also
convenient to have a spoilage detector which is not
affected by the contact with the liquid contained in the
package but the liquid is directly monitored in contact
with the device.
3. Summary o~ the Invention.
It is therefore one object of the present invention
to provide a spoilage indicating device to be added to a
f ood container in a way to provide a visual indication of
bacterial spoilage of a food product stored in the
~nnt~inc~r, the device having a pH indicator in contact with
the product through a semi-permeable membrane porous only
to selected ion -nnt~inins r~ ,lnnF~nt~ of the product.
It is still another object of the present invention
to provide a spoilage indicating device for a food
nnnt~;nl~r for providing a visual ;nf9;~t;on of bacterial
spoilage of a product comprising perishable food-stuffs and
biological preparations stored in the cnnt~;n~r, the
indicating device comprising a close cell in a wall of the
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c~-nt~in--r, the cell comprising a transparent wall
impermeable to liquids and peripherally sealed to a semi-
permeable membrane porous only to water molecules and
hydrogen ions of the product, a p~-responsive indicator
being housed in the cell, between the transparent wall and
the semi-permeable membrane, the membrane being in contact
with the product, the indicator being visible ~rom outside
the rr,nt~inPr through the transparent wall and being
selectively separated from the product by the semi-
permeable membrane which allows the ions of the product to
enter into contact with the indicator for causing the
indicator to undergo a visible reaction but preventing the
indicator f rom being hidden by the product .
It is a further object of the invention to provide
a combination of a food cr,nt~in~r and a spoilage indicating
device, the r~nt~in~r comprising a transparent impermeable
wall and the spoilage indicating device comprising a semi-
permeable membrane porous only to water molecules and
hydrogen ions of the product, a p~-responsive indicator
housed between a portion of the transparent impermeable
wall of the rrnti~inPr and the semi-permeable membrane, the
semi-permeable membrane being poriph,orally sealed to said
portion of the rnnt~inPr wall and in contact with the
product, the indicator being visible from outside the
crnt~in~r through the crlnt~in,-r transparent wall and being
separated from the product by the semi-permeable membrane
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which allows the ions of the product to enter into contact
with the indicator f or causing the indicator to undergo a
visible reaction but preventing the indicator from being
hidden by the product.
It is still a further object of the invention to
provide a combination of a food cnnt~1nPr and a spoilage
indicating device for providing a visual indication of
bacterial spoilage of a product, the cnnt~;nPr comprising
an impermeable wall including an opening formed therein,
the spoilage indicating device comprising a, close cell
~ormed by a semi-permeable membrane porous only to water
molecules and hydrogen ions of the product, and a
transparent impermeable wall sealed over the opening so
that the transparent impermeable wall of the cell seals the
opening and is outside the cnn~ nl~rl and the semi-
permeable membrane remains in contact with the product
through the opening, a pH-responsive indicator within the
cell, housed between the transparent impermeable wall and
the semi-permeable membrane of the cell, the indicator
being visible ~rom outside the cnn~;npr through the cell
transparent wall and being separated from the product by
the semi-permeable membrane which allows the ions of the
product to enter into contact wlth the indicator for
causing the indicator to undergo a visible reaction but
preventing the indicator from being hidden by the product.
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The above and other objects, features and
advantages of this invention will be better understood when
taken in connection with the acr~ ~nying drawings and
description .
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention i8 illustrated by way of
example in the following drawings wherein:
FIG. 1 is a cross-sectional view of a spoilage
indicating device of the invention;
FIG. 2 is a cross-sectional view of another
embodiment of the spoilage indicating device as mounted in
a yogurt cup;
FIG. 3 is a- cross-sectional view of the spoilage
indicating device o~ Figure 1, as mounted in a milk carton;
DESCRIPTION OF THE ~Kk~;~J EMBODI~6ENTS
Now ref erring in detail to the drawings, the
spo~lage indicating device of the invention, shown in
cross-section in Figure 1, is generally indicated by the
reference number 1 in all the applications. The novel
device includes an impermeable transparent wall 2 and a
semi-permeable porous wall 4, both walls being peripherally
sealed to each other so as to form a close cell. A pX-
responsive ;n~ ;3tor is placed inside the cell, between the
impermeable wall and the semi-permeable wall of the cell.
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Wall 2 can be made from any kind of suitable
impermeable transparent material, hard or flexible,
depending on the package or rnn~;l; nt~r to which the device
is to be added, but preferably the material is selected
from polyethylene, polypropylene, polyester or glass. Nall
4 is made of a miUlu~uoLuus semi-permeable film which
defines a selective passage to some elements of the product
to be monitored. In the case of a diary product, such as
milk, the semi-permeable film is porous only to water
molecules of the milk and the hydrogen ions carried by the
water molecules passing through the wall 4 as indicated by
the arrows in Figure 1. Wall 4 has an outer side 40 in
contact with the product under monitoring and an inner side
4i inside the cell. Membrane 4 can be made of a composite
material, cellulose, polypropylene, polyester, polyamide,
polysulphon, polytetrafluoroethylene, or ylass, all well
known in the food industry, pharmaceutical industry,
agrochemistry, chemistry, etc.
The pH-responsive indicator ~nnt~in~fl inside the
cell formed by walls 2, 4 may comprise any suitable
chemical compound or substance available in the art, such
as an indicator dye, which can be applied onto inner face
4i of wall 4 or impregnated in a support strip 3, such as a
paper or plastic strip. The indicator type and the quantity
thereof will be selected on the basis of the pH levels to
be indicated. The pH level at which the indicator will
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react will depend on the kind of product to be monitored,
milk for example, has a pH level of 6.5 to 6.6 in fresh
state. The pH level will reflect the state of the product
in connection with its consumption conditions, acidity,
physicochemical conditions, organoleptic characteristics,
etc. The indicator will be retained either on the strip or
on the semi-permeable wall in the way the chemicals are not
transferred from the cell outside into the packaged
product .
Any matter, liquid, solid or gas is prevented to
pass into device 1 through wall 2, but indicator 3 is
easily visible from outside the device so as its color
change is visually observable by the consumer before
purchasing a product or by the retailer so as the product
under a low level of ~[uality is removed from the store. As
explained above, only water molecules and hydrogen ions of
the product to be monitored can pass through membrane 4
into co~tact with indicator 3, but other components of the
product, such as polymers, colloids, proteins, starch, oil,
fat particles, which can hide the color change of the
indicator, are prevented from entering into the device and
covering the; nt~; Catnr from visibility . Spoilage indicating
device 1 may be inserted into a food cnnti:lin'~r in any way
that the device is visible from outside the nnnt;~in~r and
is preferably fixed to a wall of the cnnt~in~r as in the
arrangements shown in Figures 2, 3.
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Figure 2 is a cross sectional view of a food
container 5, a cup ~ntAi~ yogurt 7 for example, wherein
the spoilage ;n~ Atin~ device is formed by an impermeable
wall, consisting of a transparent impermeable wall 6 of the
container, to which semi-permeable membrane 4 is sealed at
peripheral edges 4e thereof to form a close cell. Indicator
3 is housed within the indicating device so as to be
isolated from the envirorment and in selected contact with
monitored product 7 through membrane 4. The color reaction
of indicator 3 can be easily observed from outside the cup
through transparent wall 6 of the cup. Indicator 3 is not
to be hidden by product 7 as f ar as only water molecules
and hydrogen ions can reach the same through the selected
pass in the semi-permeable membrane.
Figure 3 shows an alternative application of the
spoilage indicating device of the invention, in a C~-ntAin~r
having non transparent walls 8. In this case the device of
the invention could not be arranged like in the embodiment
of Figure 2 as far as the indicator would not visible
through non transparent walls 8. Under these circumstances
a window 9 is provided in wall 8 of the container over
which the spoilage indicating device of the invention is
located .
~ ike in the other disclosed embodiments, device
comprises an impermeable transparent wall 2, a semi-
permeable microporous membrane 4 peri~hPrAlly sealed to
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wall 2 and a pH-responsive indicator 3 retained between
wall 2 and membrane 4. In order to keep the rrn~inf~r
impermeable to liquids, particularly impermeable to liquid
7 stored in the cnnti~;n~rl impermeable film 2 is sealed
over window 9, against wall 8 of the rr,n~;n,~r, In order to
keep the indicator selectively exposed to contact with the
liquid to be monitored, microporous membrane 4 is sealed
and f ixed to wall 8, over window 9, so that only water
molecules and ions of product 7 can pass through membrane 4
and enter into contact with indicator 3. Like in the other
disclosed embodiments, product 7 may be any perishable
product, preferably a diary product such as milk, yogurt,
cream, etc.
Although only one indicator strip has been
disclosed and illustrated it will be obvious for any
skilled in the art that other forms may be applied ~or
example, more than one strip may be arranged, each strip
being impregnated o~ a p3~[ indicating chemical responsive to
different pX levels. In this way different and progressive
pH levels may be indicated to have a better parameter of
the state o~ freshness of a stored product.
